Wavelength-independent performance of femtosecond laser dielectric ablation spanning over three octaves

TL;DR

This study demonstrates that femtosecond laser ablation of wide bandgap dielectrics is largely wavelength-independent across a broad spectral range from UV to mid-infrared, with notable differences only at the shortest wavelength tested.

Contribution

The paper provides experimental evidence of wavelength-independent ablation thresholds over three octaves, extending understanding of ultrafast laser-material interactions and informing laser processing technologies.

Findings

Ablation thresholds form a plateau from visible to 3.5 μm wavelengths.

A significant decrease in threshold occurs at 258 nm, indicating a spectral limit.

Ablation precision and efficiency remain invariant across most of the spectral range.

Abstract

Ultrafast laser breakdown of wide bandgap dielectrics is today a key for major technologies ranging from 3D material processing in optical materials to nanosurgery. However, a contradiction persists between the strongly nonlinear character of energy absorption and the robustness of processes to the changes of the bandgap/wavelength ratio depending on applications. While various materials and bandgaps have been studied, we concentrate here the investigations on the spectral domain with experiments performed with wavelength drivers varied from deep-ultraviolet (258 nm) to mid-infrared (3.5 $\mu$m). The measured fluence thresholds for single shot ablation in dielectrics using 200-fs pulses exhibit a plateau extending from the visible domain up to 3.5-$\mu$m wavelength. This is accompanied, after ablation crater analysis, by a remarkable invariance of the observed ablation precision and efficiency. Only at the shortest tested wavelength of 258 nm, a twofold decrease of the ablation threshold and significant changes of the machining depths are detected. This defines a lower spectral limit of the wavelength-independence of the ablation process. By comparison with simulations, avalanche ionization coefficients are extracted and compared with those predicted with the Drude model. This must be beneficial to improve predictive models and process engineering developments exploiting the new high-power ultrafast laser technologies emitting in various spectral domains.